1. Field of the Invention
The present invention relates to elastic wave devices preferably for use in resonators, band-pass filters, and so on, more specifically, elastic wave devices having a structure in which another material is laminated between a support substrate and a piezoelectric layer.
2. Description of the Related Art
Elastic wave devices have been used as resonators, band-pass filters, and the like for years, and recently, they are being requested to operate at higher frequencies than before. Japanese Unexamined Patent Application Publication No. 2004-282232 discloses a surface acoustic wave device in which, on a dielectric substrate, a hard dielectric layer, a piezoelectric film, and an IDT (interdigital transducer) electrode are laminated in that order. In the disclosed surface acoustic wave device, the hard dielectric layer is disposed between the dielectric substrate and the piezoelectric film so as to raise acoustic velocity of a surface acoustic wave. As such, it is described in Japanese Unexamined Patent Application Publication No. 2004-282232 that the above configuration makes it possible for the surface acoustic wave device to operate at higher frequencies.
Japanese Unexamined Patent Application Publication No. 2004-282232 also discloses a structure in which an equal potential layer is provided between a hard dielectric layer and a piezoelectric film. The equal potential layer is formed of a metal or a semiconductor. The equal potential layer is provided so as to equalize a potential at an interface between the piezoelectric film and the hard dielectric layer.
In the surface acoustic wave device disclosed in Japanese Unexamined Patent Application Publication No. 2004-282232, it is intended to obtain a higher acoustic velocity by forming the hard dielectric layer. However, a considerably large propagation loss occurs, and the surface acoustic wave cannot be effectively confined within a piezoelectric thin film. As such, energy of the surface acoustic wave device is leaked to the dielectric substrate. This causes a problem such that characteristics of an elastic wave device are degraded.